If you have minimal space for a gearbox, coupled with a need for low-speed controlability, then this box could provide the solution.
It was designed to fit really awkward prototypes, such as vertical-boilered locomotives and tiny 0-4-0 tank engines, like the 'MRJ Project Manning Wardle'.
Even though the boxes themselves really are small, we've managed to squeeze in some big gear reductions (108:1, 80:1 and 60:1). As they use the same internal components as our bigger boxes, they're capable of transmitting power far in excess of anything the 10 Series Cans for which they were originally designed can deliver.
Output is via a 2mm axle but you can can easily bush this to 1/8in.